The present invention relates to systems for converting mechanical to electrical energy as well as providing a source of compressed air; and, more specifically, to such systems employing a relatively small engine.
In general, portable gen-sets comprising a generator and an engine, are well known. The generator typically comprises a rotor and stator arranged for relative rotation. Generally, the rotor is driven by the energy source, often mounted on the shaft of the engine. The rotor typically generates a magnetic field (using either permanent magnets or windings), which interacts with windings maintained on the stator. As the magnetic field intercepts the windings, an electrical current is generated. The induced current is typically applied to a bridge rectifier, sometimes regulated, and provided as an output. In some instances, the rectified signal is applied to an inverter to generate an AC output. Examples of portable gen-sets are described in U.S. Pat. No. 5,929,611 issued to Scott et al. on Jul. 27, 1999; U.S. Pat. No. 5,625,276 issued to Scott et al. on Apr. 29, 1997; U.S. Pat. No. 5,705,917 issued to Scott et al. on Jan. 6, 1998; U.S. Pat. No. 5,780,998 issued to Scott et al. on Jan. 14, 1998; U.S. Pat. No. 5,886,404 issued to Scott et al. on Mar. 23 1999; U.S. Pat. No. 5,900,722 issued to Scott et al. on May 4, 1999; and U.S. Pat. No. 5,929,611 issued to Scott et al. on Jan. 27, 1999, all commonly assigned with the present invention.
Portable power conversion systems find particular utility as: power sources for lights and small appliances used, for example, at construction or camping sites, or in connection with recreational vehicles; and vehicular battery charger/jump start units.
Portable compressor systems are also, in general, known. Such systems typically include: an engine; a compressor (typically a reciprocating piston pump); a drive system between the engine and the compressor; a transfer tube (conduit); a check valve; a storage reservoir (one or more tanks); a pressure regulator; and an output line terminating in an output valve. In general, the compressor intakes atmospheric air, and generates pressurized air, which is routed by the transfer conduit to the storage reservoir through the check valve. A reserve of pressurized air is thus developed in the storage reservoir. The regulator is typically disposed downstream of the storage reservoir, interposed between the reservoir and output line, with the intent that air is provided at the output valve at a predetermined regulated pressure.
These compressor systems include a mechanism for inhibiting flow of pressurized air into the reservoir once the reservoir attains a maximum pressure. They typically employ a vent valve communicating with the transfer tube on the compressor side of the check valve. When the reservoir pressure exceeds the predetermined maximum, the vent valve diverts the air from the compressor to atmosphere rather than into the reservoir. More specifically, the vent valve typically includes, or cooperates with, a pressure sensor to maintain the pressure in the reservoir within a predetermined acceptable range. The sensor is typically preset to toggle in response to upper and lower pressures in the reservoir, e.g., 100 and 130 PSI. When the reservoir is at or below the lower end of the acceptable pressure range (e.g., 100 PSI) the vent valve is closed and air from the compressor is directed into the reservoir. When the reservoir reaches the upper end of the range (e.g., 130 PSI) the vent valve is opened and air from the compressor is diverted to the atmosphere.
In many commercially available portable compressor systems, the engine operates at a constant speed (RPM) irrespective of air demand. However, compressor systems in which engine speed is varied between idle and a predetermined operating speed based upon air demand are known. In such systems, a transducer is typically used not only to control the vent valve but also to shuttle (e.g., pneumatically or mechanically) the engine throttle between idle and the predetermined operating speed positions. When the reservoir is at the lower end of the acceptable pressure range (e.g., 100 PSI) the transducer shuttles to close the vent valve and shuttles the throttle to the predetermined operating speed position. When the reservoir reaches the upper end of the range (e.g., 130 PSI) the vent valve is opened and the throttle is shuttled to a setting corresponding to idle.
Portable engine driven compressors wherein the rotational speed (angular velocity) of the engine is varied to accommodate changes in ambient conditions and reservoir pressure have been suggested. For example, U.S. Pat. No. 5,224,836 issued to Gunn et al. on Jul. 6, 1993 describes a system in which a microprocessor or microcomputer based controller receives inputs indicative of various operating temperatures, the inlet and discharge pressures of a compressor, and reservoir pressure, and adjusts the angular speed (RPM) of the engine to operate the engine at or near the minimum angular velocity (set point speed) capable of delivering a set point reservoir pressure. The set point speed is recalculated at relatively long intervals, i.e., approximately once every five minutes. While the compressor is delivering air at a selected discharge pressure and the engine is running at the set point speed, pressure control is achieved by modulation of the inlet valve of the compressor. If the reservoir set point pressure is not achievable with the engine operating at the set point speed, the engine is accelerated until either the reservoir set point pressure is achieved, or the compressor reaches a maximum operating speed. Adjustments to engine speed are effected using a proportional integral differential (PID) control function.
In systems where relatively large changes in engine speed are effected in accordance with air demand, e.g., toggling between idle and run speed, is desirable that the reservoir capacity be large enough and acceptable pressure range be wide enough to avoid short cycling between states; changing between states tends to cause increased wear on system components. Accordingly, conventional portable compressor systems typically employ relatively large reservoirs, e.g., 8 gallons capacity (typically two-gallon to four-gallon tanks, disposed horizontally in parallel underlying the compressor and engine), and a relatively wide range of acceptable pressures, e.g., 100 to 130 PSI.
Systems in which both a compressor and a generator are driven by a common engine have also been suggested. For example, an integral generator and compressor in which the armature of a generator is mounted on an extension of the rotor exclude shaft of a conventional dual rotary screw compressor is described in U.S. Pat. No. 5,242,278 issued Sep. 7, 1993 to Vanderslice et al. Further, the aforementioned U.S. Pat. No. 5,224,836 to Gunn et al. states that electronic controllers have been applied to control the angular velocity of internal combustion engine prime driver and compressor combinations which are coupled to also drive an electric generator, but that since the generator requires a substantially constant angular velocity for proper operation regardless of operating conditions, to maintain a constant frequency, the function of the controller for these internal combustion engine prime driverxe2x80x94centrifugal compressorxe2x80x94generator combinations is to produce a constant angular velocity under all conditions.
A system that provides electrical power and compressed air, according to various aspects of the present invention includes a support, an engine, a compressor, a generator, and a reservoir. The support maintains the system on a provided surface and may include wheels for portability as a hand truck. The engine may be selectively or directly coupled to the compressor. The generator is driven by the engine to provide the electrical power. A reservoir is coupled to the compressor and includes several horizontally disposed cylindrical tanks in fluid communication and arranged in one or a few vertical planes. A portion of a lower-most tank of the reservoir may be positioned below the engine; and the respective centers of gravity of the engine, the fuel tank, and the reservoir may be arranged for relatively greater stability.
A control system for the engine, generator, and compressor may provide priority response to air demand and/or priority response to electrical power demand by reducing lower priority loads on the engine prior to increasing engine speed. Consequently fuel may be conserved and run time increased.
A throttle controller moves the engine throttle from higher speed position(s) to lower speed position(s). For example, in response to low demand for compressed air in combination with low demand for electrical power, a throttle controller may move a two-position throttle. A throttle controller may include a low demand valve and throttle positioning air cylinder. The low demand valve may be operated by an electrical signal asserted in response to detecting a condition of low output current from the system.